Climate change

April 14, 2011

Fukushima rated at INES Level 7 – what does this mean?

Filed under: Japan Earthquake, Nuclear Energy — buildeco @ 8:19 pm
by Barry Brook

Hot in the news is that the Fukushima Nuclear crisis has been upgraded from INES 5 to INES 7. Note that this is not due to some sudden escalation of events  (aftershocks etc.), but rather it is based on an assessment of the cumulative magnitude of the events that have occurred at the site over the past month.

Below I look briefly at what this INES 7 rating means, why it has happened, and to provide a new place to centralise comments on this noteworthy piece of news.

The International Nuclear and Radiological Event Scale (INES) was developed by the International Atomic Energy Agency (IAEA) to rate nuclear accidents. It was formalised in 1990 and then back-dated to events like Chernobyl, Three Mile Island, Windscale and so on. Prior to today, only Chernobyl had been rated at the maximum level of the scale ‘major accident’. A useful 5-page PDF summary description of the INES, by the IAEA, is available here.

A new assessment of Fukushima Daiichi has put this event at INES 7, upgraded from earlier escalating ratings of 3, 4 and then 5. The original intention of the scale was historical/retrospective, and it was not really designed to track real-time crises, so until the accident is fully resolved, any time-specific rating is naturally preliminary.

The criteria used to rate against the INES scale are (from the IAEA documentation):

(i) People and the Environment: considers the radiation doses to people close to the location of the event and the widespread, unplanned release of radioactive material from an installation.

(ii) Radiological Barriers and Control: covers events without any direct impact on people or the environment and only applies inside major facilities. It covers unplanned high radiation levels and spread of significant quantities of radioactive materials confined within the installation.

(iii) Defence-in-Depth: covers events without any direct impact on people or the environment, but for which the range of measures put in place to prevent accidents did not function as intended.

In terms of severity:

Like the scales that describe earthquakes or major storms, each of the INES scale’s seven levels is designed to be ten times more severe that the one before. After below-scale ‘deviations’ with no safety significance, there are three levels of ‘incident’, then four levels of ‘accident’. The selection of a level for a given event is based on three parameters: whether people or the environment have been affected; whether any of the barriers to the release of radiation have been lost; and whether any of the layers of safety systems are lost.

So, on this definitional basis, one might argue that the collective Fukushima Daiichi event (core damage in three units, hydrogen explosions, problems with drying spent fuel ponds, etc.) is ~100 times worse than TMI-2, which was a Level 5.

However, what about when you hit the top of the INES? Does a rating of 7 mean that Fukushima is as bad as Chernobyl? Well, since you can’t get higher than 7 on the scale, it’s impossible to use this numerically to answer such a question on the basis of their categorical INES rating alone. It just tells you that both events are in the ‘major league’. There is simply no event rating 8, or 10, or whatever, or indeed any capacity within the INES system to rank or discriminate events within categories (this is especially telling for 7). For that, you need to look for other diagnostics.

So headlines likeFukushima is now on a par with Chernobyl‘ can be classified as semantically correct and yet also (potentially) downright misleading. Still, it sells newspapers.

There is a really useful summary of the actual ‘news’ of this INES upgrade from World Nuclear News, here. It reports:

Japanese authorities notified the International Atomic Energy Agency of their decision to up the rating: “As a result of re-evaluation, total amount of discharged iodine-131 is estimated at 1.3×1017 becquerels, and caesium-137 is estimated at 6.1×1015 becquerels. Hence the Nuclear and Industrial Safety Agency has concluded that the rating of the accident would be equivalent of Level 7.”

More here from the IAEA:

The new provisional rating considers the accidents that occurred at Units 1, 2 and 3 as a single event on INES. Previously, separate INES Level 5 ratings had been applied for Units 1, 2 and 3. The provisional INES Level 3 rating assigned for Unit 4 still applies.

The re-evaluation of the Fukushima Daiichi provisional INES rating resulted from an estimate of the total amount of radioactivity released to the environment from the nuclear plant. NISA estimates that the amount of radioactive material released to the atmosphere is approximately 10 percent of the 1986 Chernobyl accident, which is the only other nuclear accident to have been rated a Level 7 event.

I also discussed the uprating today on radio, and you can listen to the 12-minute interview here for my extended perspective.

So, what are some of the similarities and differences between Fukushima and Chernobyl?

Both have involved breeches of radiological barriers and controls, overwhelming of defence-in-depth measures, and large-scale release of radioactive isotopes into the environment. The causes and sequence of the two events were, however, very different, in terms of reactor designs, the nature of the triggering events, and time-scale for resolution — this is a topic to be explored in more depth in some future post. The obviously big contrast is in the human toll and nature of the radioactive release.

The Chernobyl event killed 28 people directly via the initial explosion or severe radiation sickness, and other ~15 died as directly attributed result of radiation-induced cancer (see the summary provided today by Ben Heard on Opinion Online: Giving Green the red light). Further, Chernobyl led to a significant overexposure of members of the public in the local area and region, especially due to iodine-131 that was dispersed by the reactor fire, and insufficient protection measures by authorities. An increase in thyroid cancers resulted from this.

In Fukushima, by contrast, no workers have been killed by radiation (or explosions), and indeed none have been exposed to doses >250 mSv (with a ~1000 mSv being the dose required for people to exhibit signs of radiation sickness, through to about 50 % of victims dying after being exposed to >5000 mSv [see chart here]). No member of the public has, as yet, been overexposed at Fukushima. Further, much of the radionuclides released into the environment around Fukushima have been a result of water leakages that were flushed into the ocean, rather than attached to carbon and other aerosols from a burning reactor moderator, where they were largely deposited on land, and had the potential to be inhaled (as occurred in Chernobyl).

So is Fukushima another Chernobyl? No. Is it a serious accident? Yes. Two quite different questions — and answers — which should not be carelessly conflated.


March 26, 2011

Preliminary lessons from Fukushima for future nuclear power plants

Filed under: IFR (Integral Fast Reactor) Nuclear Power, Japan Earthquake — buildeco @ 1:34 pm

by Barry Brook

No strong conclusions can yet be drawn on the Fukushima Nuclear Crisis, because so much detail and hard data remains unclear or unavailable. Indeed, it will probably take years to piece the whole of this story together (as has now been done for accidents like TMI and Chernobyl [read this and this from Prof. Bernard Cohen for an absolutely terrific overview]). Still, it will definitely be worth doing this post-event diagnostic, because of the valuable lessons it can teach us. In this spirit, below an associate of mine from the Science Council for Global Initiatives discusses what lessons we’ve learned so far. This is obviously a huge and evolving topic that I look forward to revisiting many times in the coming months…


Guest Post by Dr. William HannumBill worked for more than 40 years in nuclear power development, stretching from design and analysis of the Shippingport reactor to the Integral Fast Reactor. He earned his BA in physics at Princeton and his MS and PhD in nuclear physics at Yale. He has held key management positions with the U. S. Department of Energy (DOE), in reactor physics , reactor safety, and as Deputy Manager of the Idaho Operations Office.

He served as Deputy Director General of the OECD Nuclear Energy Agency, Paris, France; Chairman of the TVA Nuclear Safety Review Boards, and Director of the West Valley (high level nuclear waste processing and D&D) Demonstration Project. Dr. Hannum is a fellow of the American Nuclear Society, and has served as a consultant to the National Academy of Engineering on nuclear proliferation issues. He wrote a popular article for Scientific American on smarter use of nuclear waste, which you can download as a PDF here.



On 11 March 2011, a massive earthquake hit Japan.  The six reactors at Fukushima-Dai-ichi suffered ground accelerations somewhat in excess of design specification.  It appears that all of the critical plant equipment survived the earthquake without serious damage, and safety systems performed as designed.  The following tsunami, however, carried the fuel tanks for the emergency diesels out to sea, and compromised the battery backup systems.  All off-site power was lost, and power sufficient operate the pumps that provide cooling of the reactors and the used-fuel pools remained unavailable for over a week.  Heroic efforts by the TEPCo operators limited the radiological release.  A massive recovery operation will begin as soon as they succeed in restoring the shutdown cooling systems.

It is important to put the consequences of this event in context.  This was not a disaster (the earthquake and tsunami were disasters).  This was not an accident; the plant experienced a natural event (“Act of God” in insurance parlance) far beyond what it was designed for.  Based on the evidence available today, it can be stated with confidence that no one will have suffered any identifiable radiation-related heath effects from this event.  A few of the operators may have received a high enough dose of radiation to have a slight statistical increase in their long term risk of developing cancer, but I would place the number at no more than 10 to 50.  None of the reports suggest that any person will have received a dose approaching one Sievert, which would imply immediate health effects.

Even ignoring the possibility of hormetic effects, this is approaching the trivial when compared with the impacts of the earthquake and tsunami, where deaths will likely come to well over 20,000.  Health impacts from industrial contamination, refinery fires, lack of sanitation, etc., etc. may reasonably be supposed to be in the millions.  Even the “psychological” impacts of the Fukushima problems must be seen to pale in contrast to those from the earthquake and tsunami.

The radiological impact on workers is also small relative to the non-radiological injuries suffered by them.  One TEPCO crane operator died from injuries sustained during the earthquake. Two TEPCO workers who had been in the turbine building of Unit 4, are missing.  At least eleven TEPCO workers were take to hospital because of earthquake-related physical injuries.

TEPCO has suffered a major loss of capital equipment, the value of which is non-trivial even in the context of the earthquake and tsunami devastation.  They also face a substantial cost for cleanup of the contamination which has been released from the plants. These are financial costs, not human health and well being matters.

The Sequence of Events

Following the tsunami, the operators had no power for the pumps that circulate the primary coolant to the heat exchangers.  The only way to remove the decay heat was to boil the water in the core.  After the normal feed water supplies were exhausted, they activated the system to supply sea water to the core, knowing this would render the plant unfit to return to operation.  In this way, the reactors were maintained in a relatively stable condition, allowing the water to boil, and releasing the resulting steam to the containment building. Since this is a Boiling Water Reactor (BWR), it is good at boiling water.  Operating with the water level 1.7 to 2 meters below the top of the core, they  mimicked power operation; the core normally operates at power with the water level well below the top of the core, the top part being cooled by steam.   Cold water in, steam out, is a crude but effective means of cooling.

Before using sea water, according to reports, water levels are thought to have dropped far enough to allow the fuel to overheat, damaging some of the fuel cladding.  When overheated, the cladding (Zirconium) reacts, claiming oxygen from the water.  Water, less oxygen, is hydrogen.  When vented to the containment and then to the outer building, the hydrogen built up, and eventually exploded, destroying the enclosing building.  With compromised fuel, the steam being vented contains radioactive fission products.  The design of BWRs is such that this venting goes through a water bath (in the Torus), that filters out all but the most volatile fission products.

With time, the heat generated in used fuel (both in the core and in the fuel pool) decreases.  From an initial power of about 2% of full power an hour after shutdown (when the coolant pumps lost power) to about 0.2% a week later, the amount of steam venting decreases, and releases can be controlled and planned for favorable weather conditions.

A second concern arose because of the inability to provide cooling for the used-fuel pool in Unit 4, and later Unit 3.  The Unit 4 pool was of concern because, for maintenance, the entire core had been off-loaded into the pool in November (it is believed that two older core loadings were also in this pool, awaiting transfer to the central storage pool).  With only a few months cooling, the residual heat is sufficient to raise the temperature of the water in the pool to boiling within several days or weeks.  There is also some suggestion that the earthquake may have sloshed some water out of the pool.  In any case, the fuel pools for Units 3 and 4 eventually were thought to be losing enough water such that the fuel would no longer be adequately cooled.  Since the fuel pools are outside the primary containment, leakage from these pools can spread contamination more readily than that from the reactor core.  High-power water hoses have been used to maintain water in the fuel pools.

While many areas within the plant complex itself, and localized areas as far away as 20 Km may require cleanup of the contamination released from the reactors and from the fuel pools, there is no indication that there are any areas that will require long term isolation or exclusion.


Lessons Learned

It is not the purpose of this paper to anticipate the lessons to be learned from this event, but a few items may be noted.  One lesson will dominate all others:

Prolonged lack of electrical power must be precluded.

While the designers believed their design included sufficient redundancies (diesels, batteries, redundant connections to the electrical grid), the simultaneous extended loss of all sources of power left the operators dependant on creative responses.  This lesson is applicable both to the reactor and to fuel pools.

All nuclear installations will probably be required to do a complete review of the security of their access to electrical power.  It may be noted that this lesson is applicable to many more activities than just nuclear power.  Extended loss of electrical power in any major metropolitan area would generate a monstrous crisis.  The loss of power was irrelevant to other activities in the region near the Fukushima plant because they were destroyed by the tsunami.

Other lessons that will be learned that may be expected to impact existing plants include:

Better means of control of hydrogen buildup in the case of fuel damage may be required.

In addition, detailed examinations of the Fukushimi plants will provide evidence of the margins available in seismic protection.  Detailed reconstruction of the event will give very helpful insights into the manner that fission product can release from damaged fuel, and their transport.

Applicability of Fukushima Information to MOX-fueled Reactors:

The core of Unit 3 was fueled with plutonium recycled from earlier used reactor fuel.  Preliminary information suggests that the release of hazardous radioactive material, for this type of event, is not significantly different than that non-recycle fuel.  More detailed examinations after the damaged cores are recovered, and models developed to reconstruct the events, will be necessary to verify and quantify this conclusion.

Applicability of Fukushima Information to Gen-III Reactors:

In the period since the Fukushima plants were designed, advanced designs for BWRs (and other reactor types) have been developed to further enhance passive safety (systems feedback characteristics that compensate for abnormal events, without reliance on operator actions or on engineered safety systems), simplify designs, and reduce costs.  The results of these design efforts (referred to as Gen-III) are the ones now under construction in Japan, China and elsewhere, and proposed for construction in the U.S.

One of the most evident features of the Gen-III systems is that they are equipped with large gravity-feed water reservoirs that would flood the core in case of major disruption.  This will buy additional time in the event of a Fukushima type situation, but the plants will ultimately rely of restoration of power at some point in time.

The applicability of the other lessons (hydrogen control, fuel pool) will need to be evaluated, but there are no immediately evident lessons beyond these that will affect these designs in a major way.

Applicability of Fukushima Information to Recycling Reactors:

As noted above, Unit-III was fueled with recycled plutonium, and there are no preliminary indications that this had any bearing on the performance of this plant during this event.

Advanced recycling, where essentially all of the recyclable material is recovered and used (as opposed to recovery and recycle of plutonium) presents a different picture.  Full recycling is effective only with a fast reactor.  A metal fuel, clad in stainless steel, allows a design of a sodium-cooled fast reactor with astonishing passive safety characteristics.  Because the sodium operates far from its boiling point in an essentially unpressurized system, catastrophic events caused by leakage or pipe failures cannot occur.  The metal fuel gives the system very favorable feedback characteristics, so that even the most extreme disruptions are passively accommodated.  A complete loss of cooling, such as at Fukushima, leads to only a modest temperature rise.  Even if the control system were rendered inoperable, and the system lost cooling but remained at full power (this is a far more serious scenario than Fukushima, where the automatic shutdown system operated as designed) the system would self-stabilize at low power, and be cooled by natural convection to the atmosphere.  Should the metal fuel fail for any reason, internal fission product gases would cause the fuel to foam and disperse, providing the most powerful of all shutdown mechanisms.

The only situation that could generate energy to disperse material from the reactor is the possibility of s sodium-water reaction.  By using an intermediate sodium system (reactor sodium passes its energy to a non-radioactive sodium system, which then passes its energy to water to generate steam to turn the electrical generator), the possibility of a sodium-water reaction spreading radioactive materials is precluded.

These reactors must accommodate seismic challenges, just as any other reactor type.  While there are many such design features in common with other reactor designs, the problem is simpler for the fast reactor because of the low pressure, and the fact that this type of reactor does not need elaborate water injection systems.

In light of the Fukushima event, one must consider the potential consequences of a massive tsunami accompanying a major challenge to the reactor.  Since it may be difficult to ensure that the sodium systems remain intact under the worst imaginable circumstances, it may be prudent to conclude that a tsunami-prone location may not be the best place to build a sodium facility (whether a nuclear power plant or something else).


The major lesson to be learned is that for any water-cooled reactor there must be an absolutely secure supply of power sufficient to operate cooling pumps.  Many other lessons are likely to be learned.  At this early point, it appears that design criteria for fuel storage pools may need to be revised, and hydrogen control assessed.

Given the severity of the challenge faced by the operators at Fukushima, and their ability to manage the situation in such a way as to preclude any significant radiation related health consequences for workers or the public, this event should be a reassurance that properly designed and regulated nuclear power does not pose a catastrophic risk to the public—that, overall, nuclear power remains a safe and clean energy sources.

Given the financial impact this event will have on the utility (loss of four major power plants, massive cleanup responsibilities), it will be worthwhile for the designers, constructors, operators, and licensing authorities to support a thorough analysis of what actually transpired during this event.

March 25, 2011

10+ days of crisis at the Fukushima Daiichi nuclear power plant – 22 March 2010

Filed under: IFR (Integral Fast Reactor) Nuclear Power, Japan Earthquake — buildeco @ 1:54 pm

by Barry Brook

Update: Detailed graphical status report on each reactor unit is available. Here is the picture for Unit 2 — click on the figure to access the PDF for all units.


Yes, it really has been that long. So what happened during those 10+ days? For a long answer, look back over the daily posts on this blog, which also has plenty of links to more off-site information. For the short-hand version, I offer you this excellent graphic produced by the Wall Street Journal:

Credit: Wall Street Journal:

Things continue to develop slowly, but I think now towards an inevitable conclusion — barring any sudden turn of events, a cold shutdown (reactor temperature below 100C) should be achieved in units 1 to 3 within the next week (or two?). The other priority is to get the spent fuel storage sufficiently covered with water to make them approachable (and ideally to get AC power systems restored to these ponds, as has been the case already for units 5 and 6). The clean up, diagnostics, and ultimate decommissioning of Fukushima Daiichi, of course, will take months and years to complete.

What is the latest news?

First, there is a new estimate of the tsunami damage. According to the NEI:

TEPCO believes the tsunami that inundated the Fukushima Daiichi site was 14 meters high, the network said. The design basis tsunami for the site was 5.7 meters, and the reactors and backup power sources were located 10 to 13 meters above sea level. The company reported that the maximum earthquake for which the Fukushima Daiichi plants were designed was magnitude 8. The quake that struck March 11 was magnitude 9.

Second, the IAEA reports elevated levels of radioactivity in the sea water off the coast of these reactors. That is hardly surprising, given that contaminated cooling water would gradually drain off the site — and remember, it is very easy with modern instruments to detect radioactivity in even trace amounts. These reported amounts (see table) are clearly significantly elevated around the plant — but the ocean is rather large, and so the principle of disperse and dilute also applies.

I’m reminded of a quote from James Lovelock in “The Vanishing Face of Gaia” (2008):

In July 2007 an earthquake in Japan shook a nuclear power station enough to cause an automatic shutdown ; the quake was of sufficient severity-over six on the Richter scale-to cause significant structural damage in an average town. The only “nuclear” consequence was the fall of a barrell from a stack of low-level waste that allowed the leak of about 90,000 becquerels of radioactivity. This made front page news in Australia, where it was said that the leak posed a radiation threat to the Sea of Japan.The truth is that about 90,000 becquerels is just twice the amount of natural radioactivity, mostly in the form of potassium, which you and I carry in our bodies. In other words, if we accept this hysterical conclusion, two swimmers in the Sea of Japan would make a radiation threat.

For further details on radiation trends in Japan, read this from WNN. In short, levels are hovering at or just above background levels in most surrounding prefectures, but are elevated in some parts of Fukushima. However, the World Health Organisation:

… backed the Japanese authorities, saying “These recommendations are in line with those based on accepted public health expertise.”

Below is a detailed situation summary of the Fukushima Daiichi site, passed to me by a colleague:

(1) Radioactivity was detected in the sea close to Fukushima-Daiichi. On March 21, TEPCO detected radioactivity in the nearby sea at Fukushima-Daiichi nuclear power station (NPS). TEPCO notified this measurement result to NISA and Fukushima prefecture. TEPCO continues sampling survey at Fukushima-Daiichi NPS, and also at Fukushima-Daini NPS in order to evaluate diffusion from the Fukushima-Daiichi. Though people do not drink seawater directly, TEPCO thinks it important to see how far these radioactivity spread in the sea to assess impact to human body.
Normal values of radioactivity are mostly below detection level, except for tritium. (detection level of Co-60 is 0.02Bq/ml) Also, samples of soil in the station have been sent to JAEA (Japan Atomic Energy Agency).

(2) Seawater injection to the spent fuel pool at Fukushima-Daiichi unit 2. This continues, with seawater injected through Fuel Pool Cooling and Cleanup System (FPC) piping. A temporary tank filled with seawater was connected to FPC, and a pump truck send seawater to the tank, then fire engine pump was used to inject seawater to the pool. Although the water level in the pool is not confirmed, judging from the total amount of injected seawater, 40 tons, it is assumed that the level increased about 30 cm after this operation.

(3) Brown smoke was observed from unit 3 reactor building. At around 3:55 pm on March 21, a TEPCO employee confirmed light gray smoke arising from the southeast side of the rooftop of the Unit 3 building. Workers were told to evacuate. It is observed the smoke has decreased and died out at 6:02pm. TEPCO continues to monitor the site’s immediate surroundings. There was no work and no explosive sound at the time of discovery.

(4) Smoke from unit 2 reactor building (as of 9:00pm, March 21). TEPCO’s unit operator found new smoke spewing from mountain side of unit 2 reactor building around 6:20 pm, which was different smoke from blow-out panel on the sea side. There was no explosive sound heard at the time. At 7:10 pm, TEPCO instructed workers at unit 1 – 4 to evacuate into the building. Evacuation was confirmed at 8:30 pm.

(Note: Since there was another smoke found from unit 3 at 1:55pm and evacuation was completed at that time, no workers were remained at the units when smoke found at unit 2.)

TEPCO assumes the smoke is something like vapor, but are still investigating the cause of this smoke with monitoring plant parameters.

Radiation level near the Gate of Fukushima-Daiichi NPS increased at the time of smoke, then decreased to prior level.

5:40 pm 494 μSv/hr

6:10 pm 1,256 μSv/hr

6:20 pm 1,428 μSv/hr

6:30 pm 1,932 μSv/hr

8:00 pm 493.5 μSv/hr

As a result of smoke from unit 2 and 3, scheduled water cannon spraying operations for March 21 were postponed.

(5) Power supply restoration at unit 2 (as of 5:00 pm, March 21). Power cables have been connected to the main power center (existing plant equipment) and confirmed as properly functioning. Presently, soundness tests of the equipment are underway. A pump motor, which is used to inject water to spent fuel pool, has been identified as needing to be replaced.

Similar power connections have been made to reactors 5 and 6 and a diesel generator is providing power to a cooling pump for the used fuel pools. Power cable is being laid to reactor 4, and power is expected to be restored to reactors 3 and 4 by Tuesday.

Kyodo News now reports that all 6 units are connected to external power, and control room power and lighting is about to be restored.

The water-spraying mission for the No. 4 reactor, meanwhile, was joined by trucks with a concrete squeeze pump and a 50-meter arm confirmed to be capable of pouring water from a higher point after trial runs.

With the new pump trucks arriving, the pumping rates for water spraying has increased to 160 tonnes per hour through a 58 metre flexible boom via remote control.

Here is the latest FEPC status report:

March 21, 2011

Fukushima Nuclear Accident – Why I stay in Tokyo

Filed under: IFR (Integral Fast Reactor) Nuclear Power, Japan Earthquake — buildeco @ 12:22 pm

Posted by Barry Brook

Guest Post by Axel Lieber. Axel is a German national and has been a resident of Tokyo since 1998. He runs a small executive search firm and is married to a Japanese.

[Editor’s note: This is a personal perspective, not a professional scientific one, but I can verify Axel’s facts]

Why I stay in Tokyo

僕 が東京にとどまる理由

[This commentary contains footnotes and links that allow you to verify what I am saying.]

Thousands have left Tokyo recently in a panic about the perceived radiation threat. If you ask any one of them to precisely articulate what the threat consists of, they will be unable to do so. This is because they actually don’t know, and because in fact there is no threat justifying departure, at least not from radioactivity (*).They flee because they have somehow heard that there is a threat – from the media, their embassies, their relatives overseas, friends, etc. These sources of information, too, have never supplied a credible explanation for their advisories.

But they have managed to create a mass panic, leading to thousands of people wasting their money on expensive air fares, disrupting their professional lives, their children’s education, and the many other productive activities they were going about. In some cases, foreign executives have abandoned their post in Tokyo, guaranteeing a total loss of respect among those who have stayed behind. Some service providers catering to the foreign community have lost almost their entire income over night. Other providers reversely will lose long-term clientele because they have fled, leaving their remaining customers and clients forced to find new providers. Domestic helpers (especially from the Philippines) have suddenly lost their livelihoods because their “employers” think it’s alright to run away without paying their helpers another penny. Another result of all the hysteria is that attention has been diverted away from the real disaster: the damage done in north-eastern Japan where thousands have died, and many tens of thousands live in dreadful conditions right now, waiting for help.

Contrast this with the fact that radioactivity levels in Tokyo are entirely safe and have been since the beginning of the Fukushima incident (*1a, and *1b for continuous updates). Modern instruments to measure radioactivity are extremely sensitive and precise, and report even the smallest deviations with impressive reliability. Nowhere in the Tokyo area have there been any measurements that would imply any sort ofhealth risk. There certainly have been increases in radioactivity but they are tiny and simply irrelevant to anyone’s health. There is also no fear that there could be some kind of cover-up.

Instruments to measure radioactivity are available at many different research institutions that are not controlled by the Japanese government. The J-gov does also not control the media. They simply have no laws and no means to do so.

[Editor’s Note: For a contrast, the background level in London is 0.035 to 0.05 µSv per hour, see the pie chart for an average breakdown by source. Also, see this great chart.]

But what about a worst-case scenario, one that is yet to come? For four days now, I have tried to find a serious source of information – a nuclear safety engineer or a public health expert – who would be able to articulate just what exactly the threat to residents of Tokyo is. It has been difficult because there aren’t many who bother to. I could quote several Japanese experts here but won’t do so to avoid a debate over their credibility (which I personally do not have any particular reason to doubt). The most to-the-point assessment I have found from outside of Japan comes from the UK government’s Chief Science Advisor, Sir John Beddington. In a phone call to the British embassy in Tokyo, he says about the worst-case scenario:

In this reasonable worst case you get an explosion. You get some radioactive material going up to about 500m up into the air. Now, that’s really serious, but it’s serious again for the local area….The problems are within 30 km of the reactor. And to give you a flavour for that, when Chernobyl had a massive fire at the graphite core, material was going up not just 500m but to 30,000 feet (9,144m) . It was lasting not for the odd hour or so but lasted months, and that was putting nuclear radioactive material up into the upper atmosphere for a very long period of time. But even in the case of Chernobyl, the exclusion zone that they had was about 30km. And in that exclusion zone, outside that, there is no evidence whatsoever to indicate people had problems from the radiation. The problems with Chernobyl were people were continuing to drink the water, continuing to eat vegetables and so on and that was where the problems came from. That’s not going to be the case here. So what I would really re-emphasise is that this is very problematic for the area and the immediate vicinity and one has to have concerns for the people working there. Beyond that 20-30km, it’s really not an issue for health.(*2)

It is important to note that Beddington, too, uses language such as “really serious”. Most nuclear safety engineers at this moment would describe the Fukushima incident as “very serious” and as having potentially “catastrophic consequences”. But the important point to note here is that these descriptions of the situation do not translate into public health concerns for Tokyo residents! They apply to the local situation at and around the Fukushima plant alone.

As of the time of writing this note (March 19, 2011, 13:00 JST), the status at Fukushima is still precarious but there are now signs that the situation is stabilizing and may be brought under control in the next few days. (*3)

Tokyo, even at this time of crisis, remains one of the best, safest and coolest large cities in the world to live in. All public services operate normally or almost normally. Many areas of central Tokyo have not had any power outages, and when such occur they are limited to a few hours and certain areas, and are announced well in advance. I have personally not experienced any power outages. Food is available in almost normal quantity and quality. The only food type I have personally seen to be lacking is milk and dairy products, and rice because of panic purchases. Gas (petrol) supply is indeed limited but just yesterday I was able to get a full tank of gas after “only” a fifteen minute wait. Public order and safety in Tokyo remains higher than in any other large city in the world, as it has always been over the past few decades.

To really rub this in: if you live in New York, Shanghai, Berlin, London or Sydney or any other metropolis, you are more exposed to public safety threats such as crime or road accidents than I am at this moment, and in most cases considerably so.

Active and passive smoking, driving a car or motorcycle, getting a chest x-ray, jay-walking, or snowboarding down a snowy mountain are all much more risky activities than simply sitting on a sunny roof terrace in Tokyo.

And sunny it is today, in the capital of the country whose name is literally “Origin of the Sun”.

To obtain level-headed information about the status at Fukushima, avoid CNN and read or


(*) There is, however, a possibility that there will be further strong earthquakes in the next few weeks, especially in the north-east of Japan, but also in other areas, including Tokyo. This was demonstrated in the recent earthquakes in New Zealand and Chile, where powerful quakes followed the original ones, not necessarily in the same spot either. It would be more rational to stay away from Japan for a few weeks because of this. But again, the risk of being harmed by another earthquake, especially in Tokyo with its superb infrastructure, is not very high. And if you consider this reason enough to stay away, then indeed, you should never live in Japan because we will always face this risk here.





The original post can be read here (or here for 日本).

Fukushima nuclear accident: Saturday 19 March summary

Filed under: IFR (Integral Fast Reactor) Nuclear Power, Japan Earthquake — buildeco @ 12:18 pm

by Barry Brook

Last Saturday the the crisis level at the Fukushima Daiichi nuclear power station was rapidly on the rise. Hydrogen explosions, cracks in the wetwell torus and fires in a shutdown unit’s building — it seemed the sequence of new problems would never end. A week later, the situation remains troubling, but, over the last few days, it has not got any worse. Indeed, one could make a reasonable argument that it’s actually got better.

Yes, the IAEA has now formally listed the overall accident at an INES level 5 (see here for a description of the scales), up from the original estimate of 4. This is right and proper — but it doesn’t mean the situation has escalated further, as some have inferred. Here is a summary of the main site activities for today, followed by the latest JAIF and FEPC reports. You also might be interested in the following site map:

Another large cohort of 100 Tokyo fire fighters joined the spraying operation to cool down the reactors and keep the water in the spent fuel ponds. The ‘Hyper Rescue’ team have set up a special vehicle for firing a water cannon from 22 m high (in combination with a super pump truck), and today have been targeting the SNF pond in unit 3. About 60 tons of sea water successfully penetrated the building in the vicinity of the pool, at a flow rate of 3,000 litres per minute. Spraying with standard unmanned vehicles was also undertaken for 7 hours into other parts of the the unit 3 building (delivering more than 1,200 tons), to keep the general containment area cool. The temperature around the fuel rods is now reported by TEPCO (via NHK news) to be below 100C.

Conditions in unit 3 are stabilising but will need attention for many days to come. Promisingly, TEPCO has now connected AC cables to the unit 1 and 2 reactor buildings, with hopes that powered systems can be restored to these building by as early as tomorrow (including, it is hoped, the AC core cooling systems), once various safety and equipment condition checks are made.

Holes were made in the secondary containment buildings of Units 5 and 6 as a precautionary measure, to vent any hydrogen that might accumulate and so prevent explosions in these otherwise undamaged structures.  The residual heat removal system for these units has now been brought back on line and these pools maintain a tolerable steady temperature of 60C. More here. These buildings were operating on a single emergency diesel generator, but now have a second electricity supply via the external AC power cable.

Why are they concentrating on these activities? Let’s revisit a bit of the history of last week. The spent fuel pool still has decay heat (probably of the order of few MW in each pool) that requires active cooling. When power went out on Friday, the cooling stopped and the pool temperature has been rising slowly over the weekend, and probably started boiling off (and a large volume may have also been lost due to ‘sloshing’ during the seismic event). The pool is located on the 4th floor above the reactor vessel level. It remains unclear why they could not arrange fire trucks to deliver the sea water before the fuel rods got damaged and started releasing radioactivity. Now the effort is hampered by the high radiation level (primarily penetrating gamma rays). This is the inventory of those spent fuel ponds that have been causing so many headaches:

In order to remove the decay heat after the reactor shutdown, the cooling system should be operating. Following the loss of offsite power, the on-site diesel generators came on but the tsunami arrived an hour or so later and wiped out the diesel generators. Then the battery provided the power for 8 hours or so, during which time they brought in portable generators. However, the connectors were incompatible. As the steam pressure built up inside the pressure vessel, the relief valve was open and dumped the steam to the pressure suppression chamber, which in turn was filtered out to the confinement building and the hydrogen explosion took out the slabs.

The sea water was then pumped in by fire trucks and the reactor pressure vessels are now cooled down to near atmospheric pressure but the fuel assemblies are uncovered at the top quarter or third (the FEPC updates give the actual pressure and water levels). It appears that the pressure vessels and the reactor containment structures are intact, except the Unit 2, where the hydrogen explosion took place inside the containment and hence damaging the lower wetwell torus structure (but almost certainly not the reactor vessel, although the exact status is unclear). It appears that the radioactivity releases are mostly coming from the spent fuel storages than the reactor cores.

World Nuclear News has a really excellent extended article here entitled “Insight to Fukushima engineering challenges“. Read it! Further, you must watch this 8 minute reconstruction of the timeline of the accident done by NHK — brilliant, and really highlights the enormous stresses this poor station faced against a record-breaking force of nature. As I’d noted earlier, just about everything that could have went wrong, did. But valuable lessons must also be learned.

The IAEA and Japanese government has reported the potential contamination of food products from the local Fukushima area via radioactive iodine (mostly vented as part of the pressure relief operations of units 1 to 3). This is a short-term risk due to the 8-day half-life of radioactive iodine (and a small risk, given the trace amounts recorded), but precautions are warranted, as discussed here. What does this mean?

In the case of the milk samples, even if consumed for one year, the radiation dose would be equivalent to that a person would receive in a single CT scan. The levels found in the spinach were much lower, equivalent to one-fifth of a single CT scan.

… and to further put this in context:

The UK government’s chief independent scientific advisor has told the British Embassy in Tokyo that radiation fears from the stricken Fukushima nuclear power plant are a “sideshow” compared with the general devastation caused by the massive earthquake and tsunami that struck on 11 March. Speaking from London in a teleconference on 15 March to the embassy, chief scientific officer John Beddington said that the only people likely to receive doses of radiation that could damage their health are the on-site workers at the Fukushima Daiichi plant. He said that the general population outside of the 20 kilometre evacuation zone should not be concerned about contamination.

As to the possibility of a zirconium fire in the SNF ponds, this seems unlikely. Zr has a very high combustion point, as illustrated in video produced by UC Berkeley nuclear engineers. They applied a blowtorch to a zirconium rod and it did not catch on fire. The demonstration is shown about 50 seconds into this video. The temperature was said to reach 2000C [incidentally, I visited that lab last year!].

The the Japan Atomic Industrial Forum has provided their 12th reactor-by-reactor status update (16:00 March 19).

Here is the latest FEPC status report:


  • Radiation Levels
    • At 7:30PM on March 18, radiation level outside main office building (approximately 1,640 feet from Unit 2 reactor building) of Fukushima Daiichi Nuclear Power Station: 3,699 micro Sv/h.
    • Measurement results of ambient dose rate around Fukushima Nuclear Power Station at 4:00PM and 7:00PM on March 18 are shown in the attached two PDF files respectively.
    • At 1:00PM on March 18, MEXT decided to carry out thorough radiation monitoring nationwide.
    • For comparison, a human receives 2,400 micro Sv per year from natural radiation in the form of sunlight, radon, and other sources. One chest CT scan generates 6,900 micro Sv per scan.
  • Fukushima Daiichi Unit 1 reactor
    • Since 10:30AM on March 14, the pressure within the primary containment vessel cannot be measured.
    • At 4:00PM on March 18, pressure inside the reactor core: 0.191MPa.
    • At 4:00PM on March 18, water level inside the reactor core: 1.7 meters below the top of the fuel rods.
    • As of 3:00PM on March 18, the injection of seawater continues into the reactor core.
    • Activities for connecting the commercial electricity grid are underway.
  • Fukushima Daiichi Unit 2 reactor
    • At 4:00PM on March 18, pressure inside the primary containment vessel: 0.139MPaabs.
    • At 4:00PM on March 18, pressure inside the reactor core: -0.002MPa.
    • At 4:00PM on March 18, water level inside the reactor core: 1.4 meters below the top of the fuel rods.
    • As of 3:00PM on March 18, the injection of seawater continues into the reactor core.
    • Activities for connecting the commercial electricity grid are underway.
  • Fukushima Daiichi Unit 3 reactor
    • At 2:00PM on March 18, six Self Defense emergency fire vehicles began to shoot water aimed at the spent fuel pool, until 2:38PM (39 tones of water in total).
    • At 2:42PM on March 18, TEPCO began to shoot water aimed at the spent fuel pool, until 2:45PM, by one US Army high pressure water cannon.
    • At 3:55PM on March 18, pressure inside the primary containment vessel: 0.160MPaabs.
    • At 3:55PM on March 18, pressure inside the reactor core: -0.016MPa.
    • At 3:55PM on March 18, water level inside the reactor core: 2.0 meters below the top of the fuel rods.
    • As of 3:00PM on March 18, the injection of seawater continues into the reactor core.
  • Fukushima Daiichi Unit 4 reactor
    • No official updates to the information in our March 18 update have been provided.
  • Fukushima Daiichi Unit 5 reactor
    • At 4:00PM on March 18, the temperature of the spent fuel pool was measured at 152.4 degrees Fahrenheit.
  • Fukushima Daiichi Unit 6 reactor
    • At 4:00PM on March 18, the temperature of the spent fuel pool was measured at 148.1 degrees Fahrenheit.
  • Fukushima Daiichi Common Spent Fuel Pool
    • At 10:00AM on March 18, it was confirmed that water level in the pool was secured.
  • Fukushima Daiichi Dry Cask Storage Building
    • At 10:00AM on March 18, it was confirmed that there was no damage by visual checking of external appearance.

At 5:50PM on March 18, Japanese Safety Authority (NISA: Nuclear and Industrial Safety Agency) announced provisional INES (International Nuclear and Radiological Event Scale) rating to the incidents due to the earthquake.

Fukushima Daiichi Unit 1, 2 and 3 Unit = 5 (Accident with wider consequences)

Fukushima Daiichi Unit 4 = 3 (Serious incident)

Fukushima Daini Unit 1, 2 and 4 Unit = 3 (Serious incident)

(No official provisional rating for Fukushima Daini Unit 3 has been provided.)

March 17, 2011

Fukushima Nuclear Accident – 16 March update

Filed under: IFR (Integral Fast Reactor) Nuclear Power, Japan Earthquake — buildeco @ 7:53 am

by Barry Brook

This is an update of the situation as of 10 am JST Wednesday 16 March. (For background on events of 15 March and earlier, start with previous posts and included links.) Note that this is a blog, not a news website, and thus the following analysis, like all others on this, is a mixture of news and opinion — but facts remain paramount.

First, the situation is clearly (but slowly) stabilising. As each day passes, the amount of thermal heat (caused by radioactive decay of the fission products) that remains in the reactor fuel assemblies decreases exponentially. When the reactors SCRAMed on 11 March after the earthquake, and went sub-critical, their power levels dropped by about 95 % of peak output (the nuclear fission process was no longer self-sustaining). Over the past 5 days, the energy in the fuel rods dropped by another ~97 %, such that the heat dissipation situation is getting more and more manageable. But we’re not out of the woods yet, and the reactor cores will need significant cooling for at least another 5 days before stability can be ensured.

Yesterday there appears to have been a fracture in the wetwell torus (see diagram: that circular structure below and to the side of the reactor vessel) in Unit 2, caused by a hydrogen explosion, which led to a rapid venting of highly radioactive fission product gases (mostly noble [chemically unreactive] gases, the majority of which had a half-life of seconds to minutes). It also caused a drop in pressure in the supression pool, which made the cooling process more challenging. However, despite some earlier concerns, it is now clear that containment was not breached. Even under this situation of extreme physical duress, the multiple containment barriers have held firm. This is an issue to be revisited, when the dust finally settles.

Units 1 and 3, the other two operating reactors at Fukushima Daiichi when the earthquake struck, continue to be cooled by sea water. Containment is secure in both units. However, like Unit 2, there is a high probability that the fuel assemblies have likely suffered damage due to temporary exposure (out of water), as the engineers struggled over the last few days to maintain core coolant levels. Whether there has been any melting of the clad or rods remains unclear, and probably will continue to be shrouded in a cloud of uncertainty for some time yet.

The other ongoing serious issue is with managing the heat dissipation in the spent fuel ponds. These contain old fuel rods from previous reactor operation that are cooling down, on site, immersed in water, which also provides radiation shielding. After a few years of pond cooling, these are transferred to dry storage. The heat in these rods is much less than those of the in-core assemblies, but it is still significant enough as to cause concern for maintaining adequate coverage of the stored fuel and to avoid boiling the unpressurised water. There have been two fires in Unit 4, the first tentatively linked to a failed oil pump, and the second, being of (currently) unknown cause, but the likelihood is that it was linked to hydrogen gas bubbling.

There appears to have been some exposure of this spent fuel, and radiation levels around this area remain high — making access in order to maintain water levels particularly troublesome. Note that apart from short-lived fission product gases, these radiation sources are otherwise contained within the rods and not particularised in a way that facilitates dispersion. Again, the problems encountered here can be linked to the critical lack of on-site power, with the mains grid still being out of action. As a further precaution, TEPCO is considering spraying the pool with boric acid to minimise the probability of ‘prompt criticality’ events. This is the news item we should be watching most closely today.

An excellent 2-page fact sheet on the spent fuel pool issues has been produced by the NEI, which can be read here: Used Nuclear Fuel Storage at the Fukushima Daiichi Nuclear Power Plant (this includes an explanation of what might happen under various scenarios).

This figure illustrates the current reported state of the Daiichi and Daini reactors, last updated 1230 on 16 March (click to enlarge):

The status report from the The Federation of Electric Power Companies of Japan (FEPC) is given below:

• Radiation Levels

o At 10:22AM (JST) on March 15, a radiation level of 400 milli sievert per hour was recorded outside secondary containment building of the Unit 3 reactor at Fukushima Daiichi Nuclear Power Station.

o At 3:30PM on March 15, a radiation level of 596 micro sievert per hour was recorded at the main gate of Fukushima Daiichi Nuclear Power Station.

o At 4:30PM on March 15, a radiation level of 489 micro sievert per hour was recorded on the site of the Fukushima Daiichi Nuclear Power Station.

o For comparison, a human receives 2400 micro sievert per year from natural radiation in the form of sunlight, radon, and other sources. One chest CT scan generates 6900 micro sievert per scan.

• Fukushima Daiichi Unit 1 reactor

o As of 10:00PM on March 14, the pressure inside the reactor core was measured at 0.05 MPa. The water level inside the reactor was measured at 1.7 meters below the top of the fuel rods.

• Fukushima Daiichi Unit 2 reactor

o At 6:14AM on March 15, an explosion was heard in the secondary containment building. TEPCO assumes that the suppression chamber, which holds water and stream released from the reactor core, was damaged.

o At 1:00PM on March 15, the pressure inside the reactor core was measured at 0.608 MPa. The water level inside the reactor was measured at 1.7 meters below the top of the fuel rods.

• Fukushima Daiichi Unit 3 reactor

o At 6:14AM on March 15, smoke was discovered emanating from the damaged secondary containment building.

• Fukushima Daiichi Unit 4 reactor

o At 9:38AM on March 15, a fire was discovered on the third floor of the secondary containment building.

o At 12:29PM on March 15, TEPCO confirmed extinguishing of the fire.

• Fukushima Daini Units 1 to 4 reactors: all now in cold shutdown, TEPCO continues to cool each reactor core.

This indicates a peak radiation level of 400 mSv/hr, which has come down to about 0.5 mSv/hr by the afternoon. This ‘spot’ radiation level was measured at a location between Unit 3 and 4. It was attributted to a hydrogen explosion in the spent fuel pool of Unit 4 — but this is still under debate. The radiation level at the site boundary is expected to have been much lower and, to date, there is no risk to the general public.

Two other useful sources of information are from the WNNRadiation decreasing, fuel ponds warming and Second fire reported at unit 4. ANS Nuclear Cafe continues to be a great collator of key official channels and top news stories.

Finally, this is a useful perspective from an MIT staffer that is well worth reading:

What happened at the Fukushima reactor? Events in Japan confirm the robustness of modern nuclear technology — not a failure

Kirk Sorenson, from Energy from Thorium blog, also has this very interesting piece: Thoughts on Fukushima-Daiichi. A concluding excerpt:

What is known is that this is a situation very different than Chernobyl or Three Mile Island. There was no operator error involved at Fukushima-Daiichi, and each reactor was successfully shut down within moments of detecting the quake. The situation has evolved slowly but in a manner that was not anticipated by designers who had not assumed that electrical power to run emergency pumps would be unavailable for days after the shutdown. They built an impressive array of redundant pumps and power generating equipment to preclude against this problem. Unfortunately, the tsunami destroyed it.

There are some characteristics of a nuclear fission reactor that will be common to every nuclear fission reactor. They will always have to contend with decay heat. They will always have to produce heat at high temperatures to generate electricity. But they do not have to use coolant fluids like water that must operate at high pressures in order to achieve high temperatures. Other fluids like fluoride salts can operate at high temperatures yet at the same pressures as the outside. Fluoride salts are impervious to radiation damage, unlike water, and don’t evolve hydrogen gas which can lead to an explosion. Solid nuclear fuel like that used at Fukushima-Daiichi can melt and release radioactive materials if not cooled consistently during shutdown. Fluoride salts can carry fuel in chemically-stable forms that can be passively cooled without pumps driven by emergency power generation. There are solutions to the extreme situation that was encountered at Fukushima-Daiichi, and it may be in our best interest to pursue them.

More updates as further information comes to hand. Otherwise, for me, it’s back to the mad TV and radio media circus.

UPDATE: From World Nuclear News: Problems for units 3 and 4

Chief Cabinet Secretary Yukio Edano had outlined problems that had occured on the morning of 16 March with Fukushima Daiichi 3 and 4.

At 8:34am local time white smoke was seen billowing out of Fukushima Daiichi 3. Efforts to determine the cause of this development were interrupted as all workers had evacuated to a safe area due to rising radiation readings. Readings from a sensor near the front gate had fluctuated for some time, although Edano said that on the whole there was no health hazard. Earlier in the morning readings had ranged between 600-800 microsieverts per hour, but at 10am readings rose to 1000 microsieverts per hour. Readings began to fall again from around 10:54.

Edano said that one possibility being considered was that the unit 3 reactor had suffered a similar failure to that suffered by unit 2 yesterday, although there had been no reported blast or loud sound, which had been the case for unit 2. The immediate focus, said Edano was on monitoring of levels and checking pumping operations.

Edano also outlined plans for units 4-6. Preparations were being made to inject water into unit 4, however the high levels of radiation from unit 3 were imparing those preparations. When possible, the water injection would be done gradually as there were safety concerns over pouring a large amount of water at once. The water will be pumped into the reactor building from the ground, plans to drop water from a helicopter having been abandoned. Although he said that “all things were possible” Edano did not believe that recriticality at unit 4 was a realistic risk

Second fire at unit 4

Earlier, the Nuclear and Industrial Safety Agency said that a blaze was spotted in the reactor building of Fukushima Daiichi 4 at 5.45am local time this morning.

Attempts to extinguish it were reportedly delayed due to high levels of radiation in the area. A spokesperson for TEPCO said that by around 6:15am there were no flames to be seen.

The incident at unit 4 is believed to be in the region of a used fuel pond in the upper portion of the reactor building.


Tokyo Electric Power Company issued a notice of an explosion at unit 4 at 6am on 15 March. This was followed by the company’s confirmation of damage around the fifth floor rooftop area of the reactor building.

On that day, a fire was discovered but investigations concluded it had died down by around 11am.

At present it is not clear whether today’s fire was a completely new blaze, or if the fire reported yesterday had flared up again.

Think climate when judging nuclear power

Filed under: IFR (Integral Fast Reactor) Nuclear Power, Japan Earthquake — buildeco @ 7:50 am

by Barry Brook

Guest Post by Ben Heard. Ben is Director of Adelaide-based advisory firm ThinkClimate Consulting, a Masters graduate of Monash University in Corporate Environmental Sustainability, and a member of the TIA Environmental and Sustainability Action Committee. After several years with major consulting firms, Ben founded ThinkClimate and has since assisted a range of government, private and not-for profit organisations to measure, manage and reduce their greenhouse gas emissions and move towards more sustainable operations. Ben publishes regular articles aimed at challenging thinking and perceptions related to climate change at

(Editorial Note: [Barry Brook]: Ben is a relatively recent, but very welcome friend of mine, who is as passionate as I am about mitigating climate change. I really appreciate publishing his thoughts in this most difficult of times. Now, more than ever, we must stand up for what we believe is right]


On 8th March, I delivered a presentation to around 45 people, describing my journey from a position of nuclear power opponent to that of nuclear power proponent. The presentation was very well received and has generated much interest.

Just four days later, I saw those first appalling images of the tsunami hitting Japan, and realised that for the first time since 1986, a nuclear emergency situation was unfolding.

In all cases, I find it most distasteful when individuals or groups push agendas in the face of unfolding tragedy. Let me say at the outset that this is not my intention.

Sadly, many people and groups don’t share this sentiment, including a great many who have wasted no time in making grave and unfounded pronouncements regarding the safety of nuclear power, and how this event should impact Australia’s decision making in energy. This has been aided no end by a media bloc that has reflected the general state of ignorance that exists regarding nuclear power, as well as a preference for headlines ahead of sound information at this critical time. The whole situation has been all too predictable, but still most disappointing. It has reinforced one of the great truisms in understanding how we humans deal with risk: We are outraged and hyper-fearful of that which we do not understand, rather than that which is likely to do us harm. Rarely if ever are they the same thing.

Those who attended my presentation on the 8th March will have seen that I place a high value on two things in forming an opinion and making a decision: Facts and context. Facts without context can be dangerously misleading. In this newsletter therefore, I would like to present some of the basic facts and context of this event, as well as providing links to reliable and up-to-date sources of information to gain a more detailed understanding of the crisis. From there, I only ask that you maintain a critical frame of mind in considering the true implications of this event.

Firstly, the context. Japan is a densely populated chain of islands. It is the fourth largest economy in the world, and derives around 30% of its electricity from 55 nuclear reactors at 17 locations around the country. Japan has been using nuclear power for some time. As such some of the reactors are approaching 40 years of age, and are older designs by comparison with what would be built today.

On 11th March, Japan experienced an earthquake measuring 9.0 on the Richter Scale. The Richter Scale is logarithmic, meaning a 9 quake is ten times more powerful than an 8, 100 times more powerful than a 7 and so on. On this basis the quake was something like 100,000 times the force of that which struck Christchurch recently. It is only the 4th quake of greater than 9 magnitude in recorded history.

Just one hour later, a tsunami measuring up to 10 metres struck large parts of the Japanese coast. We have all seen the awesome and terrifying footage of this wave, which laid waste to nearly everything in its path.

So by way of context, what I would like you to do is take Japan’s population density, coastal geography and high penetration of nuclear energy. Then overlay a two-phase natural catastrophe, with only one hour between each phase. Each phase of the catastrophe is perhaps the most powerful of its kind that we will see in our lifetimes.

I am sure those of you who have ever conducted risk assessment exercises will agree that it would be difficult to construct, in our wildest imaginings, a scenario that would pose a more comprehensive and arduous test of the operational safety of nuclear power plants in the world today.

Lets now turn to the response of Japan’s nuclear power industry to this event, sticking at this stage to high level facts that are not in any way in dispute:

• When the earthquakes struck, Japan’s nuclear power stations did as they were designed to do and shut down with the insertion of control rods. This halted the nuclear chain reaction that generates the power. In response the plants rapidly dropped in power to around 5% of normal.

• Other (non-uranium) constituents of the fuel remained “hot” i.e. reacting, which is normal.

• Back up power systems (diesel generators) were applied to continue to provide cooling to the reactor core. This worked as expected.

• Approximately 1 hour later, two power plants housing seven nuclear reactors were struck by a 7 metre tsunami. These plants were Fukushima Daiichi and Fukushima Daini. This disabled the diesel generators that were in use, and all other back-up generators that were available. It is this second disaster that triggered the problems at these power plants, as the plants began to experience a loss of cooling on the fuel.

• Back-up cooling from batteries was applied, and provided cooling for approximately a further 8 hours

• Other measures have then needed to be implemented as this power source ran out. This has included pumping sea-water into the reactor core. This is not a preferred action as it causes some damage.

• Some portions of the fuel rods remained exposed from the coolant for long enough to heat up and melt. This is the meaning of “partial meltdown”

• Some build up of radioactivity has occurred within the reactor buildings. This has been periodically vented in a controlled way to maintain pressure within the reactor at a safe level. The radiation being vented is of a type that is short lived, decaying rapidly to harmless substances

• The venting gas has contained hydrogen. Unfortunately, perhaps due to not venting quickly enough, the hydrogen concentrations have become elevated and resulted in explosions occurring outside of the reactor building when the venting occurred

• Presently the reactor cores are being successfully cooled and progressively moved to a state of cold shutdown, meaning fully under control.

• Critically, throughout the disaster the integrity of the very strong Containment Structures, which separate the nuclear reactor from the outside world, has been maintained. The reactor building itself then contains the core of nuclear fuel, and these reactor buildings have also remained intact. This means there has never been a risk of a “Chernobyl-type” incident, with serious releases of radioactivity to the surrounding environment that would pose a threat to human health. The Chernobyl power stations had no such structure, which greatly increased the consequences of that accident.

• The incident has received a severity rating of INES 6. It is clearly very serious. The Three Mile Island Accident was a 5. Chernobyl, however, was a 7 (the highest), and is a very different league.

For more detailed and technical information regarding these events, please look through and follow the regular updates and review some of the other excellent, more technical postings

There seems to be some suggestion that “but for the efforts” of the engineers, this situation would be worse. Well, that’s true, but at the same time, misleading. Passive safety is a great thing, be it nuclear power plants or the cars we drive. But at the end of the day, a key control measure in catastrophic events will always be a skilled and well trained work force with the knowledge and ability to respond to a changing situation. That’s as true for the power plants as for the rest of the country, where the army, police and other emergency services will play a vital role in mitigating the damage.

The bottom line of the events at Fukushima and the nuclear power sector more broadly would appear to be as follows:

• Zero deaths from radiation

• Zero release of radiation levels of a danger to human health, except for brief periods for those working within the plant compound (not Public exposure). These workers would be well protected and monitored to avoid excessive accumulated doses

• Minimal injuries (about a dozen) as a result of the hydrogen explosions

• No significant or lasting environmental impact whatsoever

• A major evacuation, which has no doubt been distressing for all involved

• 8 — 10 of Japan’s 55 nuclear reactors known to have varying levels of damage that will impact their ability to provide electricity. The remainder will no doubt require inspection, but would appear to be relatively undamaged.

The main contribution of note from the nuclear power sector has been dangerously misleading headlines and media reports, and a distraction from the greater tragedy unfolding in Japan, which is likely to have caused fatalities in the 10,000s, and left great areas of the country in total wreck and ruin.

So, combining the extraordinary context with that high level summary of facts, what conclusion should be drawn about the current and future role of nuclear power, particularly with regard to operational safety?

That is up to each of you, and I don’t want to push an agenda. If you want my conclusion, read on.

If Japan’s nuclear power sector can withstand the worst natural calamity I hope to ever see in my life and contribute no deaths, minimal injuries and minimal environmental impact, then nuclear power must be just about the sturdiest, best designed, best managed and least dangerous infrastructure in the world. And in a world that is quickly cooking itself through climate change, nuclear power must not be allowed to suffer from the hype, headlines and hyperbole that have stemmed from this tragic event.

Fear or facts. I choose facts. I hope you do too.

March 15, 2011

Fukushima Nuclear Accident – 15 March summary of situation

Filed under: IFR (Integral Fast Reactor) Nuclear Power, Japan Earthquake — buildeco @ 11:37 pm

by Barry Brook

The situation surrounding the Fukushima Nuclear Accident, triggered by Japan’s largest recorded earthquake and the resulting 10 m high tsunami, continues to develop rapidly. This post is intended to be a concise update of the situation as of 12pm Japan Standard Time, 15 March 2011. For a summary of the situation prior to today, read these posts:

Japanese nuclear reactors and the 11 March 2011 earthquake

Fukushima Nuclear Accident – a simple and accurate explanation (with further updates at MIT here:

Japan Nuclear Situation – 14 March updates

Further technical information on Fukushima reactors

TEPCO reactor by reactor status report at Fukushima

This is also a useful summary, from William Tucker (published in the Wall Street Journal): Japan Does Not Face Another Chernobyl. See also:  Nuclear Overreactions: Modern life requires learning from disasters, not fleeing all risk.


Attention has centred on units #1, 2 and 3 of the Fukushima Daiichi plant (all Boiling Water Reactors built in the 1970s). Current concern is focused on unit #2 (more below). Units 4, 5 and 6 at the site were not in service at the time of the earthquake and their situation is stable.

At a nearby plant, Fukushima Daiini, the situation is now under control, and units are in, or approaching, cold shutdown. I do not expect any further significant developments at that site. To quote WNN:

In the last 48 hours, Tepco (Tokyo Electric Power Company) has carried out repairs to the emergency core coolant systems of units 1, 2 and 4 and one by one these have come back into action. Unit 1 announced cold shutdown at 1.24 am today and unit 2 followed at 3.52 am. Repairs at unit 4 are now complete and Tepco said that gradual temperature reduction started at 3.42pm. An evacuation zone extends to ten kilometres around the plant, but this is expected to be rescinded when all four units are verified as stable in cold shutdown conditions.

Fukushima Daini Unit 1 reactor

o As of 1:24AM on March 14, TEPCO commenced the cooling process after the pumping system was restored.

o At 10:15AM on March 14, TEPCO confirmed that the average water temperature held constant below 212 degrees Fahrenheit.

Fukushima Daini Unit 2 reactor

o At 7:13AM on March 14, TEPCO commenced the cooling process.

o As of 3:52PM on March 14, the cooling function was restored and the core temperature was stabilized below 212 degrees Fahrenheit.

• Fukushima Daini Unit 3 reactor

o As of 12:15PM on March 13, reactor has been cooled down and stabilized.

• Fukushima Daini Unit 4 reactor

o At 3:42PM on March 14, cooling of the reactor commenced, with TEPCO engineers working to achieve cold shutdown.

The rest of this post will focus on the ongoing crisis situation at Fukushim Daiichi. Let me underscore the fact that accurate information is sparse, uncertain and rapidly changing.

During March 12 and 13, there were serious issues with providing sufficient cooling to units 1 and 3 after the tsunami had caused damage to the diesel backup generators and compromised the emergency cooling water supply. This resulted in a decision to use sea water injection to keep the reactors cool — a process that is ongoing. Steam was regularly vented as part of the effort to relieve steam pressure within the reactor vessels, but this also led to an accumulation of hydrogen gas within the secondary buildings that house the reactor units. Possible sources for the hydrogen are discussed here. Unfortunately, this hydrogen could not be vented sufficiently quickly, resulting in chemical explosions (hydrogen-oxygen interactions) within the two reactor housing buildings of both unit 1 and unit 2 during March 12-13.

The roof and part of the side walls of both buildings were severely damaged as a result. After the first hydrogen explosion there is no longer a roof on the building, so there is little chance of any large buildup of hydrogen or further explosions at these units. [In restrospect, the designers (40 years ago) perhaps should have more carefully considered the implications of the decision to vent the pressure suppression torus to the reactor building space]. Although hydrogen recombiners are a standard feature of that design, they unfortunately lost all AC power, and then the batteries were run down. Containment (the robust concrete shell and 18 inch thick steel reactor vessel within it), however, remained intact. This was verified by monitoring levels of radiation surrounding the units — if there had been any containment breach, levels would have jumped.

This cutaway diagram shows the central reactor vessel, thick concrete containment and lower torus structure in a typical boiling water reactor of the same era as Fukushima Daiichi 2

This is an overview of the current status of units 1 to 3:

Radiation Levels

o At 9:37AM (JST) on March 14, a radiation level of 3130 micro sievert was recorded at the Fukushima Daiichi Nuclear Power Station.

o At 10:35AM on March 14, a radiation level of 326 micro sievert was recorded at the Fukushima Daiichi Nuclear Power Station.

o Most recently, at 2:30PM on March 15, a radiation level of 231 micro sievert was recorded at Fukushima Daiichi Nuclear Power Station.

Fukushima Daiichi Unit 1 reactor

o As of 12:00AM on March 15, the injection of seawater continues into the primary containment vessel.

Fukushima Daiichi Unit 2 reactor

o At 12:00PM on March 14, in response to lower water levels, TEPCO began preparations for injecting seawater into the reactor core.

o At 5:16PM on March 14, the water level in the reactor core covered the top of the fuel rods.

o At 6:20PM on March 14, TEPCO began to inject seawater into the reactor core.

o For a short time around 6:22PM on March 14, the water level inside the reactor core fell below the lower measuring range of the gauge. As a result, TEPCO believes that the fuel rods in the reactor core might have been fully exposed.

o At 7:54PM on March 14, engineers confirmed that the gauge recorded the injection of seawater into the reactor core.

o At 8:37PM on March 14, in order to alleviate the buildup of pressure, slightly radioactive vapor, that posed no health threat, was passed through a filtration system and emitted outside via a ventilation stack from Fukushima Daiichi Unit 2 reactor vessel.

Fukushima Daiichi Unit 3 reactor

o At 11:01AM on March 14, an explosion occurred at Fukushima Daiichi Unit 3 reactor damaging the roof of the secondary containment building. Caused by the interaction of hydrogen and oxygen vapor, in a fashion to Unit 1 reactor, the explosion did not damage the primary containment vessel or the reactor core.

o As of 12:38AM (JST) on March 15, the injection of seawater has been suspended.

What is of most current concern?

Units 1 and 3: the situation now seems fairly stable. There is some concern that holding pools for spent nuclear fuel (SNF) may have been damaged by the hydrogen explosions, but nothing is confirmed. Provided the pool walls remain unbreached and the SNF is covered with water, the situation should not escalate. Note: Although still ‘hot’, the SNF decay heat is many orders of magnitude lower than the fuel assemblies within reactors 1 to 3.

Unit 4: A fire has started at the building of Unit #4. Note that the reactor of this unit is stable and was not operating at the time of the earthquake.

Kan also confirmed a fire burning at unit 4, which, according to all official sources, had never been a safety concern since the earthquake. This reactor was closed for periodic inspections when the earthquake and tsunami hit, therefore did not undergo a rapid and sudden shutdown. It was of course violently shaken and subject to the tsunami.

Shikata said that there had been “a sign of leakage” while firefighters were at work, “but we have found out the fuel is not causing the fire.” The fire is now reported extinguished.

Unit 2: This is now of most concern, and the situation continues to change quickly. Here is the key information to hand (I will update as new data emerges).

Loud noises were heard at Fukushima Daiichi 2 at 6.10am this morning. A major component beneath the reactor is confirmed to be damaged. Evacuation to 20 kilometres is being completed, while a fire on site has now been put out.

Confirmation of loud sounds at unit 2 this morning came from the Nuclear and Industrial Safety Agency (NISA). It noted that “the suppression chamber may be damaged.” It is not clear that the sounds were explosions.

The pressure in the pool was seen to decrease from three atmospheres to one atmosphere after the noise, suggesting possible damage. Radiation levels on the edge of the plant compound briefly spiked at 8217 microsieverts per hour but later fell to about a third that.

A close watch is being kept on the radiation levels to ascertain the status of containment. As a precaution Tokyo Electric Power Company has evacuated all non-essential personnel from the unit. The company’s engineers continue to pump seawater into the reactor pressure vessel in an effort to cool it.

Evacuation ordered

Prime minister Naoto Kan has requested that evacuation from 20 kilometer radius is completed and those between 20-30 kilometers should stay indoors. He said his advice related to the overall picture of safety developments at Fukushima Daiichi, rather than those at any individual reactor unit.

Shortly afterwards Noriyuki Shikata said radiation levels near the reactors had reached levels that would affect human health. It is thought that the fire had been the major source of radiation.

Prime minister Naoto Kan has requested that everyone withdraw from a 30 kilometer evacuation zone around the nuclear power plant and that people that stay within remain indoors. He said his advice related to the overall picture of safety developments at Fukushima Daiichi, rather than those at any individual reactor unit.

Regarding radiation levels: It is very important to distinguish between doses from the venting of noble-gas fission products, which rapidly dissipate and cause no long-term contamination or ingestion hazard, and aerosols of other fission products including cesium and iodine.

From NEI:

Yukio Edano, Japan’s Chief Cabinet Secretary, during a live press conference at 10 p.m. EDT, said there is a fire at Fukushima Daiichi 4 that is accompanied by high levels of radiation between Units 3 and 4 at the site. The fire began burning at Unit 4 at around 6 a.m. Japan time on March 14 and is still burning. Fire fighters are responding to the fire. The reactor does not have fuel in the reactor, but there is spent fuel in the reactor (pool) and Edano said that he assumes radioactive substances are being released. “The substances are coming out from the No. 4 reactor and we are making the utmost effort to put out the first and also cool down the No. 4 reactor (pool).”

Edano said that a blast was heard this morning at Unit 2 at about 6:30 a.m. A hole was observed in the number 2 reactor and he said there is very little possibility that an explosion will occur at Unit 2.

“The part of the suppression chamber seems to have caused the blast,” Edano said. A small amount of radioactive substance seems to have been released to the outside.

TEPCO workers continue to pump sea water at 1, 2 and 3 reactors. “The biggest problem is how to maintain the cooling and how to contain the fire at No. 4.” At 10:22 a.m. Japan time, the radiation level between units 2 and 3 were as high as 40 rem per hour. “We are talking about levels that can impact human health.” Edano said.

Of the 800 staff that remained at the power plant, all but 50 who are directly involved in pumping water into the reactor have been evacuated.

More updates to the above as the fog of uncertainty begins to clear…


Finally, a telling comment from a friend of mine in the US nuclear research community:

The lesson so far: Japan suffered an earthquake and tsunami of unprecedented proportion that has caused unbelievable damage to every part of their infrastructure, and death of very large numbers of people. The media have chosen to report the damage to a nuclear plant which was, and still is, unlikely to harm anyone. We won’t know for sure, of course, until the last measure to assure cooling is put in place, but that’s the likely outcome. You’d never know it from the parade of interested anti-nuclear activists identified as “nuclear experts” on TV.

From the early morning Saturday nuclear activists were on TV labelling this ‘the third worst nuclear accident ever’. This was no accident, this was damage caused by truly one of the worst of earthquakes and tsunamis ever. (The reported sweeping away of four entire trains, including a bullet train which apparently disappeared without a trace, was not labelled “the third worst train accident ever.”) An example of the reporting: A fellow from one of the universities, and I didn’t note which one, obviously an engineer and a knowlegable one, was asked a question and began to explain quite sensibly what was likely. He was cut off after about a minute, maybe less, and an anti-nuke, very glib, and very poorly informed, was brought on. With ponderous solemnity, he then made one outrageous and incorrect statement after another. He was so good at it they held him over for another segment

The second lesson is to the engineers: We all know that the water reactor has one principal characteristic when it shuts down that has to be looked after. It must have water to flow around the fuel rods and be able to inject it into the reactor if some is lost by a sticking relief valve or from any other cause – for this, it must have backup power to power the pumps and injection systems.

The designers apparently could not imagine a tsunami of these proportions and the backup power — remember, the plants themselves produce power, power is brought in by multiple outside power lines, there are banks of diesels to produce backup power, and finally, banks of batteries to back that up, all were disabled. There’s still a lot the operators can do, did and are doing. But reactors were damaged and may not have needed to be even by this unthinkable earthquake if they had designed the backup power systems to be impregnable, not an impossible thing for an engineer to do. So we have damage that probably could have been avoided, and reporting of almost stunning inaccuracy and ignorance.Still, the odds are that no one will be hurt from radioactivity — a few workers from falling or in the hydrogen explosions, but tiny on the scale of the damage and killing around it.

It seems pathetic that Russia should be the only reported adult in this — they’re quoted as saying “Of course our nuclear program is not going to be affected by an earthquake in Japan.” Japan has earthquakes. But perhaps it will be, if the noise is loud enough.

TEPCO reactor by reactor status report at Fukushima

Filed under: IFR (Integral Fast Reactor) Nuclear Power, Japan Earthquake — buildeco @ 11:34 pm

by Barry Brook

Current status of reactors, from TEPCO (will update as required, click to enlarge)

Further technical information on Fukushima reactors

Filed under: IFR (Integral Fast Reactor) Nuclear Power, Japan Earthquake — buildeco @ 11:33 pm

by Barry Brook

Below is edited material sent to me in confidence from some colleagues in the professional nuclear engineering and research community. It provides some further insight into what is going on at Fukushima, and what is still unknown.

The main document was written by one nuclear engineer; the quotes are the response from another engineer.


1. Likely timeline of incident is:

a. Reactors 1, 2 and 3 were in operation at Fukushima Daiichi nuclear power plant when the earthquake struck.

b. all three reactors were shut down and control rods were inserted when earthquake struck.

c. Cooling was maintained to remove decay heat

d. decay heat drops rapidly on reactor shut down (e.g a 3GW reactor will reduce to 200MW decay heat after 1s and 50MW after 1 hour… But takes long time (3-6months!) to reduce to negligible levels)

e. sometime (≈1hr) later tsunami struck and mains power was lost to coolant circuit on Unit 1

f. Diesel generators also failed when tsunami hit so cooling was run by backup batteries for 7-8 hours

g. Other emergency diesel generators brought in but insufficient to run pumps

h. loss of coolant leads to fuel rods no longer being cooled by two phase flow (it is a Boiing water Reactor) and eventually get hot enough to recat with steam to produce Hydrogen.

{While this is plausible it would suggest massive loss of Pressure Vessel (PV) generated steam beyond the containment boundary (since the explosion did not disrupt the containment). In my view a far more plausible explanation is that hydrogen routinely injected in the Make Up Water System to control the corrosives (mainly O2) produced by radiolysis was released suddenly and catastrophically from outside the containment and within the reactor building. In reacting with oxygen from the atmosphere within the building at the correct concentration of hydrogen (4-74%) only a spark is required to detonate a hydrogen oxygen explosion.

By contrast the spontaneous splitting of water to hydrogen and oxygen requires a temperature of greater than 2000 C in the absence of a catalyst. The normal radiolytic environment of a BWR core produces an excess of oxygen, not hydrogen. Given that the explosion reduced the source term, by all accounts, the reaction with hydrogen for Make UP water injection is a likely scenario and potentially the most plausible explanation for such an explosion at present. This could be even more plausible and verifiable if the Daiichi plants were not retrofitted with Noble metal corrosivity reduction systems (Pt) which have been implemented in many BWRs to reduce site hydrogen inventory. Even with noble metal systems there is still a significant hydrogen inventory external to the containment in BWRs to manage the corrosivity of PV water}

i. Gas pressure in steel reactor pressure vessel rises when coolant systems are not active and is vented to reactor building by engineers. {In my view there is not yet plausible evidence that the temperature of the PV water was sufficiently high to spontaneously split water}

j. The hydrogen in the reactor building is ignited in an explosion which blows out the walls but is not likely to have damaged Steel pressure vessel or concrete containment.

{this is true of both scenarios –but the source of the hydrogen is also external to the PV and containment in my explanation, overcoming the problem of why there was not a hydrogen explosion within the containment and outside the PV!}

k. Operators are now flooding reactor with borated sea water. Would only do this of they had run out of demineralised water – and were sure that water was not spontaneously being split in the PV.

2. Other relevant observations

a. These reactors are old generation I GE BWR’s nearing the end of their useful life so economic loss would not be large: but decommissioning and decontamination costs may be significant.

b. Some reports say 50-100cm of fuel was above coolant. Not necessarily serious in BWR but hydrogen explosion suggests some of the core got very hot

{wrong explanation in my view}!

c. No evidence of catastrophic loss of fuel element integrity yet. BWR fuel often gets small leaks and fission fragments enter water! Only relatively low levels of Cs and I reported so far suggesting fuel integrity still OK.

d. Increase in Cs and I would accompany fuel element breakdown and eventual meltdown.

e. A parallel series of event may now be happening in Unit 3.

f. MOX fuel may have been in one of these reactors

g. to a first approximation there is no difference on the present context between conventional and MOX fuel

h. If anything, the MOX should be marginally more benign for a radiological point of view than UO2 based fuel. It may have a higher toxicological risk however.

3. It is expected that enough coolant and power will be found to avoid meltdown. In which case it could be argued that this is a reasonable result for 50 year old Gen I Reactors exposed to the worst earthquake and tsunami for 100+ years!

4. If meltdown does occur fuel should melt through to concrete basement spread and eventually cool. Not a good result but hopefully, predictable.

5. These events would not happen in modern reactors which are designed to be cooled on shutdown by natural convection.


Response: H2 (production due to oxidation of Zircalloy by high temp steam has to be seriously considered in all full or partial LOCA (loss of coolant accident) scenarios, so I remain conservatively suspicious.

Reply: You then still have to explain why the primary event chain for PV generated H2 and O2 which is 1) PV to containment, then 2) containment (no explosion in the containment) prior to 3) venting to atmosphere!!! (which would in any event be to the stack via filters not via the reactor building)!!! The video footage of the explosion was clearly a fast H2/O2 (shockwave evident) and asymmetrical event– blast leaves to screen left – which implies a concentrated source of H2 mixing with oxygen (Make Up water inventory) rather than a diluting source into atmosphere via the stack which would have taken out the filters at least and increased rather than deceased the site boundary source term.

But I agree very hot Zircalloy in steam is a plausible low temperature route to H2/O2, but remember that the temperature is decay heat not fission generated so radiolysis to produce extra O2 will be many orders of magnitude below that of an operating BWR. I’ll regard a PV chain as more plausible if you can explain how hydrogen (very light stuff) got from containment to reactor building – possible with certain piping configurations…I guess.

Unit 1 was the GE BWR design. These references might assist:

Radiochemistry in Nuclear Power Reactors (1996) Commission on Physical Sciences, Mathematics, and Applications

BWR water chemistry – a delicate balance (2000) British Nuclear Societ

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